<template>
  <view :id="elId" class="v-tabs" :style="{
    background: bgColor,
    padding
  }">
    <scroll-view :scroll-x="scroll" :scroll-left="scroll ? scrollLeft : 0" :scroll-with-animation="scroll">
      <view class="v-tabs__container" :style="{
        display: scroll ? 'inline-flex' : 'flex',
        whiteSpace: scroll ? 'nowrap' : 'normal',
        height
      }">
        <view
          class="v-tabs__container-item" v-if="i!=2"
          v-for="(v, i) in tabs"
          :key="i"
          :style="{
            color: current == i ? activeColor : color,
            fontSize: current == i ? fontSize : fontSize,
            fontWeight: bold && current == i ? 'bold' : '',
            justifyContent: !scroll ? 'center' : ''
          }"
          @click="change(i)"
        >
          {{ field ? v[field] : v }}
        </view>
        <view v-if="!pills" class="v-tabs__container-line" :style="{
          background: lineColor,
          width: lineWidth + 'px',
          height: lineHeight,
          borderRadius: lineRadius,
          left: lineLeft + 'px',
          transform: `translateX(-${lineWidth / 2}px)`
        }"></view>
        <view v-else class="v-tabs__container-pills" :style="{
          background: pillsColor,
          borderRadius: pillsBorderRadius,
          left: pillsLeft + 'px',
          width: currentWidth + 'px',
          height
        }"></view>
      </view>
    </scroll-view>
  </view>
</template>

<script>
/**
 * v-tabs
 * @property {Number} value 选中的下标
 * @property {Array} tabs tabs 列表
 * @property {String} bgColor = '#fff' 背景颜色 
 * @property {String} color = '#333' 默认颜色
 * @property {String} activeColor = '#2979ff' 选中文字颜色
 * @property {String} fontSize = '28rpx' 默认文字大小 
 * @property {String} activeFontSize = '28rpx' 选中文字大小 
 * @property {Boolean} bold = [true | false] 选中文字是否加粗
 * @property {Boolean} scroll = [true | false] 是否滚动
 * @property {String} height = '60rpx' tab 的高度
 * @property {String} lineHeight = '10rpx' 下划线的高度
 * @property {String} lineColor = '#2979ff' 下划线的颜色
 * @property {Number} lineScale = 0.5 下划线的宽度缩放比例
 * @property {String} lineRadius = '10rpx' 下划线圆角
 * @property {Boolean} pills = [true | false] 是否胶囊样式
 * @property {String} pillsColor = '#2979ff' 胶囊背景色
 * @property {String} pillsBorderRadius = '10rpx' 胶囊圆角大小
 * @property {String} field 如果是对象，显示的键名
 *
 * @event {Function(current)} change 改变标签触发
 */
export default {
  props: {
    value: {
      type: Number,
      default: 0
    },
    tabs: {
      type: Array,
      default () {
        return []
      }
    },
    bgColor: {
      type: String,
      default: '#fff'
    },
    padding: {
      type: String,
      default: '0'
    },
    color: {
      type: String,
      default: '#333'
    },
    activeColor: {
      type: String,
      default: '#2979ff'
    },
    fontSize: {
      type: String,
      default: '28rpx'
    },
    activeFontSize: {
      type: String,
      default: '32rpx'
    },
    bold: {
      type: Boolean,
      default: true
    },
    scroll: {
      type: Boolean,
      default: true
    },
    height: {
      type: String,
      default: '70rpx'
    },
    lineColor: {
      type: String,
      default: '#2979ff'
    },
    lineHeight: {
      type: String,
      default: '10rpx'
    },
    lineScale: {
      type: Number,
      default: 0.5
    },
    lineRadius: {
      type: String,
      default: '10rpx'
    },
    pills: {
      type: Boolean,
      deafult: false
    },
    pillsColor: {
      type: String,
      default: '#2979ff'
    },
    pillsBorderRadius: {
      type: String,
      default: '10rpx'
    },
    field: {
      type: String,
      default: ''
    }
  },
  data () {
    return {
      elId: '',
      lineWidth: 30,
      currentWidth: 0, // 当前选项的宽度
      lineLeft: 0, // 滑块距离左侧的位置
      pillsLeft: 0, // 胶囊距离左侧的位置
      scrollLeft: 0, // 距离左边的位置
      containerWidth: 0, // 容器的宽度
      current: 0 // 当前选中项
    }
  },
  watch: {
    value (newVal) {
      this.current = newVal
      this.$nextTick(() => {
        this.getTabItemWidth()
      })
    },
    current (newVal) {
      this.$emit('input', newVal)
    },
    tabs(newVal) {
      this.$nextTick(() => {
        this.getTabItemWidth()
      })
    }
  },
  methods: {
    // 产生随机字符串
    randomString (len) {
      len = len || 32
      let $chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678'    /****默认去掉了容易混淆的字符oOLl,9gq,Vv,Uu,I1****/
      let maxPos = $chars.length
      let pwd = ''
      for (let i = 0; i < len; i++) {
        pwd += $chars.charAt(Math.floor(Math.random() * maxPos))
      }
      return pwd
    },
    // 切换事件
    change (index) {
      if (this.current !== index) {
        this.current = index
        
        this.$emit('change', index)
      }
    },
    // 获取左移动位置
    getTabItemWidth () {
      let query = uni.createSelectorQuery()
      // #ifndef MP-ALIPAY
        .in(this)
      // #endif
      // 获取容器的宽度
      query.select(`#${this.elId}`).boundingClientRect((data) => {
        if (!this.containerWidth) {
          this.containerWidth = data.width
        }
      }).exec()
      // 获取所有的 tab-item 的宽度
      query.selectAll('.v-tabs__container-item').boundingClientRect((data) => {
        if (!data) {
          return
        }
        let lineLeft = 0
        let currentWidth = 0
        if (data) {
          for (let i = 0; i < data.length; i++) {
            if (i < this.current) {
              lineLeft += data[i].width
            } else if (i == this.current) {
              currentWidth = data[i].width
            } else {
              break
            }
          }
        }
        // 当前滑块的宽度
        this.currentWidth = currentWidth
        // 缩放后的滑块宽度
        this.lineWidth = currentWidth * this.lineScale * 1
        // 滑块作移动的位置
        this.lineLeft = lineLeft + currentWidth / 2
        // 胶囊距离左侧的位置
        this.pillsLeft = lineLeft
        // 计算滚动的距离左侧的位置
        if (this.scroll) {
          this.scrollLeft = this.lineLeft - this.containerWidth / 2
        }

      }).exec()
    }
  },
  mounted () {
    this.elId = 'xfjpeter_' + this.randomString()
    this.current = this.value
    this.$nextTick(() => {
      this.getTabItemWidth()
    })
  }
}
</script>

<style lang="scss" scoped>
.v-tabs {
  width: 100%;
  box-sizing: border-box;
  overflow: hidden;

  &__container {
    position: relative;
    display: inline-flex;
    align-items: center;
    white-space: nowrap;
    overflow: hidden;

    &-item {
      display: flex;
      align-items: center;
      height: 100%;
      position: relative;
      z-index: 10;
      flex: 1;
      padding: 0 11px;
      transition: all 0.3s;
      white-space: nowrap;
    }

    &-line {
      position: absolute;
      bottom: 0;
      transition: all 0.3s linear;
    }

    &-pills {
      position: absolute;
      top: 0;
      transition: all 0.3s linear;
      z-index: 9;
    }
  }
}

/deep/ ::-webkit-scrollbar {
  display: none;
}
</style>
